a-a a-b a-t aaa aab aad aaf aas aat ab- aba abb abd abf abs abt ad- ada adb add adf ads adt af- afa afb afd aff afs aft as- asa asb asd asf ass ast at- ata atb atd atf ats att baa bab bad baf bas bat bba bbb bbd bbf bbs bbt bda bdb bdd bdf bds bdt bfa bfb bfd bff bfs bft bsa bsb bsd bsf bss bst bta btb btd btf bts btt daa dab dad daf das dat dba dbb dbd dbf dbs dbt dda ddb ddd ddf dds ddt dfa dfb dfd dff dfs dft dsa dsb dsd dsf dss dst dta dtb dtd dtf dts dtt faa fab fad faf fas fat fba fbb fbd fbf fbs fbt fda fdb fdd fdf fds fdt ffa ffd fff ffs fft fsa fsb fsd fsf fss fst fta ftb ftd ftf fts ftt saa sab sad saf sas sat sba sbb sbd sbf sbs sbt sda sdb sdd sdf sds sdt sfa sfb sfd sff sfs sft ss- ssa ssb ssd ssf sss sst sta stb std stf sts stt taa tab tad taf tas tat tba tbb tbd tbf tbs tbt tda tdb tdd tdf tds tdt tfa tfb tfd tff tfs tft tsa tsb tsd tsf tss tst tta ttb ttd ttf tts ttt